Felipe Nasr says he didn't want to wait for 2015 F1 deal

The Brazilian was confirmed as a Sauber race driver for 2015 on Wednesday, and he will partner Marcus Ericsson at the team.

But the GP2 race winner said that having to wait around for other potential vacancies, such as those at Lotus or Force India, was a risk.

"Well, there was a lot of waiting in other teams," said Nasr when asked why he chose Sauber.

"There is so much to go around, it's not only about having a good car, it's the whole package, and Sauber seemed to add up for me."

Nasr has no doubts that Sauber will be stronger next season and is unconcerned about joining a team that has failed to score so far in 2014.

"I have to say they had a difficult year, but I believe there will be some improvements next year," he said.

"Technically speaking, we know Sauber still has to improve and from one year to the other things can change.

"I believe they will change for the better on the engine side and the car being better developed.

"I expect them to improve in all areas."

Nasr also paid tribute to the experience he has gained as Williams reserve driver this season.

He has completed five Friday practice outings for the team, most recently this morning's session at Interlagos, with one more scheduled for the season-ending Abu Dhabi Grand Prix, as well has having two days of testing.

"It made me a more prepared driver in all kinds of ways," he said.

"For me to be running as a reserve driver and having a few opportunities to drive the car all builds up for me to be ready to take this challenge.

"So I have to thank Williams for the opportunity and for all the experience they have provided me."

When asked whether it is possible that he could make an early debut for Sauber, possibly in the post-Abu Dhabi GP F1 test, the Brazilian said he has "not heard anything at the moment".